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Why isn’t sizeof for a struct equal to the sum of sizeof of each member?
I can not understand why is it like this:
#include <stdio.h>
#include <stdlib.h>
typedef struct
{
char b;
int a;
} A;
typedef struct
{
char b;
} B;
int main() {
A object;
printf("sizeof char is: %d\n",sizeof(char));
printf("sizeof int is: %d\n",sizeof(int));
printf("==> the sizeof both are: %d\n",sizeof(int)+sizeof(char));
printf("and yet the sizeof struct A is: %d\n",sizeof(object));
printf("why?\n");
B secondObject;
printf("pay attention that the sizeof struct B is: %d which is equal to the "
"sizeof char\n",sizeof(secondObject));
return 0;
}
I think I explained my question in the code and there is no more need to explain. besides I have another question: I know there is allocation on the: heap/static heap/stack, but what is that means that the allocation location is unknown, How could it be ?
I am talking about this example:
typedef struct
{
char *_name;
int _id;
} Entry;
int main()
{
Entry ** vec = (Entry**) malloc(sizeof(Entry*)*2);
vec[0] = (Entry *) malloc(sizeof (Entry));
vec[0]->_name = (char*)malloc(6);
strcpy (vec[0]->_name, "name");
vec[0]->_id = 0;
return 0;
}
I know that: vec is on the stack. *vec is on the heap. *vec[0] is on the heap. vec[0]->id is on the heap.
but : vec[0]->_name is unknown why ?
